Summary Veltion Therapeutics LLC (VTP) is developing novel, potent and specific inhibitors of ATF4 as antifibrotic agents, utilizing radiation-induced intestinal and lung fibrosis as initial, proof-of-concept indications in the preventive setting. Veltion Therapeutics is collaborating with Dr. Constantinos Koumenis at the University of Pennsylvania, a pioneer in oncology research and the pro-tumorigenic and pro-metastatic role of ATF4 as well as for screening and developing radioprotectors and mitigators. He has published extensively on the pathobiology of radiation-induced fibrosis, and has collaborated extensively with co-I, Dr. Melpo Christofidou- Solomidou on chemical-induced fibrosis. One of the major limitations of chemo/radiotherapy is the toxicity in normal tissues such as the intestine and lung, in the form of ulceration, bleeding, pneumonitis and fibrosis, which is mostly associated with the irreversible end-stage chronic inflammation. Moreover, fibrosis is also an important characteristic of pancreatic (PanCa) and lung cancers that has been shown to correlate with worse disease outcomes. Activated fibroblasts have been characterized as the major cell type that contribute to the onset and manifestation of intestinal and lung fibrosis post-chemoradiation. Preliminary results using a conditional knockout ATF4 model showed a strong positive correlation between ATF4 expression and functional activation of fibroblasts, characterized by ATF4-dependent regulation of collagen levels and deposition. Veltion Therapeutics LLC believes that disrupting ATF4 activity with small molecule inhibitors could lead to inhibition of the onset and progression of fibrosis. Our team has developed a robust cell-based screen and is completing screening of a curated library of 44,000 preselected small molecules. With the first 2,500 compounds screened, we have identified 8 compounds with IC50 in the low µM range against ATF4. In this application, we propose to: (a) Expand our assay for inhibitors of ATF4 activity to a 44,000 compound library and validate the specificity and potency of 30-50 identified inhibitors in in vitro assays for collagen production and deposition (b) Use the 3 most effective inhibitors to determine their MTD and efficacy in mouse models of radiation-induced fibrosis. Positive results from these studies will form the basis of PK/PD and toxicity studies as well as broader testing against chemotherapy- induced fibrosis in additional models of fibrosis in a Phase II STTR. The team, postulates that the proposed work will lead to better protection of normal tissues rendering chemo/radiotherapy treatments more effective against malignancies and improve the quality of life of millions of cancer patients.